This invention is in the field of plug-in electronic circuit board assemblies, and more specifically, mechanical aids for plug-in board insertion and extraction.
Since the advent of the transistor, circuit boards which plug into a socket in electronic equipment have been common. They are often used to provide quick and easy access to circuit functions and for easy replacement for circuits which have failed. In addition, in some equipment, plug-in circuit boards are used to alter the function of the equipment, i.e., to provide options. In telecommunication multiplexing equipment, plug-in boards are also used to grow capacity. A channel bank, for example, may combine as many as 96 individual telephone channels onto one trunk, but the full capacity may not be needed for several years. The bank may be purchased with only enough plug-in channel units for immediate demand, with additional units ordered as the need arises.
In perhaps the most common type electrical connection for plug-in boards, a portion of the board along its leading edge forms the plug. Electrical contacts on the surface of the plug section of the board are connected to the board circuitry. When the circuit board is inserted into the equipment frame, the plug section of the board enters a socket, and spring-loaded contacts in the socket individually bear against the board contacts to complete all of the circuits.
With the remarkable progress of the past decade in the number of components that can be integrated on a single silicon chip, the amount of circuitry mounted on a circuit board has also increased many times. This naturally results in more and more connections needed between the board and the socket. While ten years ago one might expect twenty connections per board, more recent designs are apt to require over 150. Since the socket spring pressure required to make good contact is the same for each contact, the force required to insert a circuit board into an equipment frame socket increases directly with the number of contacts. It is therefore possible to require as much as 100 pounds of force to insert a board into a socket containing 198 contacts.
It is known in the art to use various latching levers to provide mechanical advantage to generate these high forces. What has turned a relatively simple problem in mechanical advantage into a much more difficult problem in accurate contact alignment, however, is the fact that the circuit boards themselves have shrunk while the number of contacts per board has increased. This has resulted in very close spacing between contacts. When boards and sockets are manufactured to economically achievable tolerances, it is all too likely that the contacts on the inserted board will not mate properly with the contacts in the socket. In fact, unless extreme care is used in inserting and extracting the board, open and short circuits and cross-connections can occur. Furthermore, socket contacts can be permanently bent out of shape by even slight vertical board movement during insertion or extraction. Needless to say, the high forces which must be overcome due to the large number of connections exacerbate the inaccuracy of the insertion process.
An object of this invention, however, is a circuit board assembly that includes a novel lever arrangement for smooth and accurate insertion even into a high density socket.
A second object is a circuit board assembly that provides smooth and easy extraction.
A third object is a circuit board assembly in which the lever arrangement is also a faceplate, and still another object is a circuit board assembly in which the faceplate lever also latches.